This invention relates to a high inner pressure and heavy duty pneumatic radial tire having an improved belt construction for effectively improving durability of the tire to be typically used for aircraft and the like.
With pneumatic radial tires used with high inner pressure under heavy loads, it is generally considered that belts consisting of a plurality of cord reinforcing layers are needed. In order to sufficiently support high pressure with a minimum number of belts particularly in a pressure-resistance test (which requires the ability to resist a pressure of four times a used pressure) for pneumatic radial tires of aircraft, it has been generally considered that cords of the belts should be arranged substantially in parallel with an equatorial plane. Such an arrangement of belts is often called a "circumferential belt construction". With the circumferential belt construction, however, elongation and contraction of the belts are difficult when the tire is rolling because of the particular cord arrangement. As a result, shoulder portions of a tread of the tire are dragged on a road because of outer diameters of shoulder portions being smaller than that at the center of the tread. Therefore, it is very disadvantageous for avoiding irregular wear.
Accordingly, the belt construction of cord reinforcing layers whose cords intersect with each other between the layers has been mainly used. With pneumatic radial tires such as aircraft tires used with high inner pressure under heavy loads, however, belts are subjected to great forces so that separations starting from ends of cords located at side edges of the belts are likely to occur in case of the belt construction using the intersecting cord reinforcing layers.
In order to mitigate stress concentrations causing such separations at ends of cords, it has been proposed to fold the cord reinforcing layers at the side edges of the belts. Even when using such a folding construction, the separations are not sufficiently prevented for tires such as aircraft tires which are repeatedly used by replacing worn treads plural times for a long time. Such a disadvantage results from the difference in rigidity between the folded portions, and rubber thereabout. Therefore, the durability of a tire using the folding construction is not sufficient.